In vessels for molten metal having a discharge port which is controlled by a gate valve or the like, the port is frequently plugged. An unplugging apparatus is disclosed in U.S. Pat. No. 4,450,986 to Harasym et al. The unplugging apparatus disclosed in that patent provides a simple, reliable and inexpensive device which facilitates unplugging the discharge port while being safe and inhibiting contamination of the molten metal. The unplugging apparatus includes a conduit which extends through the wall of an annular member to a lance housing disposed within the annular member. The conduit introduces pressurized gas into the housing. The upper end portion of the lance housing includes a frustrum shaped portion and a reduced diameter cylindrical portion which guides upward movement of a tube. The tube carries a charge of combustible material. The upper end portion of the lance housing must be fabricated to strict tolerances to ensure that the tube longitudinal axis does not become skewed with respect to the longitudinal axis of the housing during travel of the tube. A skewed condition could result in binding contact between the bottom portion of the tube and the interior surface of the housing.
The tube has a nozzle tip provided with an opening for discharging pressurized gas and a cylindrical bottom portion provided with an opening for admitting the pressurized gas. The reduced diameter portion of the lance housing is elongated so that the relative lengths of the tube and housing are such that the tube does not leave the housing as it travels upwardly to contact plugged material in the vessel discharge port. A pressurized combustible gas such as oxygen is introduced through the conduit into the lance housing to propel the tube upwardly into contact with the material plugging the discharge port. Heat from the material plugging the discharge port ignites the gas discharging at the tip of the tube. If the pressure of the gas at the tip of the tube is too great, e.g. 250 psi, the discharging gas produces a chilling effect tending to inhibit ignition of the charge of combustible material.
The problems solved by the present invention are those of simplifying the fabrication of the lance housing while ensuring that the tube is retained in the housing during upward travel without contacting the interior surface of the housing, and eliminating the chilling effect of pressurized gas at the upper end of the tube so as to ensure ignition of the charge of combustible material.